How cannabis affects you, the risks, plus where to find help if you are trying to quit weed.

Cannabis (also known as marijuana, weed, dope or grass) is the most widely used illegal drug in the UK, although its use in recent years has fallen.

The proportion of 11-15 year olds in England who had used cannabis in the last year fell from 13.3% in 2003 to 7% in 2013. The proportion of 16-59 year olds using cannabis in the last year has fallen from 10.6% in 2003-04 to 6.6% in 2013-14.

How cannabis makes you feel

The effects of cannabis vary from person to person:

some people may feel chilled out, relaxed and happy

others get the giggles or become more talkative

hunger pangs are common – this is sometimes known as "getting the munchies"

you may become more aware of your senses – colours may look more intense and music may sound better

it’s common to feel as though time is slowing down

Cannabis can have other effects too:

it makes some people feel faint and/or sick – this is sometimes known as a "whitey"

it can make you feel sleepy and lethargic

some people find it affects their memory, making it harder to remember things

it makes some people feel confused, anxious or paranoid, and some experience panic attacks and hallucinations. These effects are particularly common with stronger forms of cannabis, such as skunk and sinsemilla

If you use cannabis regularly it can make you demotivated and uninterested in other things going on in your life, such as education or work. Long-term use can affect your ability to learn and to concentrate.

Can you get addicted to cannabis?

In the past cannabis wasn’t thought to be addictive. However, research has shown that it can be addictive, particularly if you have been using it regularly for quite a while. About 10% of regular cannabis users are thought to become dependent.

As with other addictive drugs such as cocaine and heroin, you can develop a tolerance to it. This means you have to have more and more to get the same effects. If you stop taking it, you can experience withdrawal symptoms, such as cravings, difficulty sleeping, mood swings, irritability and restlessness.

If you regularly smoke cannabis with tobacco, you’re likely to get addicted to nicotine and may develop tobacco-related illnesses, such as cancer and coronary heart disease. If you cut down or give up, you will experience withdrawal from nicotine as well as cannabis.

Risks associated with cannabis

Recent research has helped us better understand the health risks from using cannabis. We know that:

Cannabis affects your ability to drive. This is one of the reasons why drug driving, like drink driving, is illegal. One French study found that drivers who had been using cannabis were more than twice as likely to cause a fatal car crash.

If you smoke it, cannabis can be harmful to your lungs. Like tobacco, it contains cancer-causing chemicals (carcinogens) that increase your risk of lung cancer. It can also make asthma worse, and cause wheezing in people without asthma. If you mix cannabis with tobacco and smoke it, the risks to your lungs are higher.

Cannabis can harm your mental health. Regular use is associated with an increased risk of developing a psychotic illness, such as schizophrenia. A psychotic illness is one where you experience hallucinations (when you see things that aren’t really there) and delusions (when you believe things that aren’t really true). Your risk of developing a psychotic illness is higher if you start using cannabis in your teens and if you have a family history of mental illness. Cannabis use has also been shown to increase the risk of a relapse in people who have schizophrenia, and could make existing symptoms worse.

Cannabis may affect your fertility. Research done in animals suggests that cannabis can disrupt sperm production in males and ovulation in females.

If you are pregnant, cannabis may harm your unborn baby. Research suggests that using cannabis during pregnancy could affect your baby's brain development. Regularly smoking cannabis with tobacco is associated with an increased risk of your baby being born small or premature.

Does my age affect my risks?

The risks linked to using cannabis do seem to be higher for people who use it regularly from an early age, including the risk of developing a mental illness.

It’s not clear why the risks are higher for people who start using cannabis when young. It may be linked to the fact that, during the teenage years, the brain is still forming its connections and cannabis interferes with this process.

Does cannabis have medicinal benefits?

Herbal cannabis contains many different compounds, called cannabinoids, which have different effects. Two of these cannabinoids – tetrahydrocannabinol (THC) and cannabidiol (CBD) – are the active ingredients of a prescribed drug called Sativex. Currently this is only licensed in the UK as a treatment to relieve the pain of muscle spasms in multiple sclerosis.

Further research is under way to test the effectiveness of cannabis-based drugs for a range of other conditions including the eye disease glaucoma, appetite loss in people with HIV or AIDS, epilepsy in children and pain associated with cancer. We won’t know whether or not these treatments are effective until trials have concluded.

Does cannabis lead to other drugs?

While most people who use harder drugs like heroin have used cannabis, only a small proportion of people who use cannabis go on to use hard drugs. However, buying cannabis brings you into contact with the illegal drugs trade, making it more likely that you will be exposed to other drugs.